裂缝系统气藏动态储量计算新方法——以四川盆地蜀南地区茅口组气藏为例

A new method of dynamic reserves calculation for gas reservoirs in fracture networks: A case study of the reservoir in Maokou Group,Shunan Block,Sichuan Basin

四川盆地蜀南地区下二叠统茅口组气藏具有储层非均质性强、缝洞系统发育、地层水活跃、生产动态特征复杂等特征。部分裂缝系统在实际生产过程中,压降曲线异常上翘或弯曲,表现出存在复杂储集体、异常能量补充的现象,表明储集空间发生变化。而常规动态方法多局限于定容储集体动态储量计算,对储集空间发生变化、存在地层水侵影响的裂缝系统,动态储量计算结果差异大,方法适应性较差。为此,综合考虑气藏地质特征、气水分布模式及生产动态等因素,根据产量不稳定分析方法的原理,采用Topaze生产分析软件精细刻画地质模型、数值求解等方法,以S47井裂缝系统为例,计算得到了不同生产阶段各储集体的动态储量,结果能够反映客观实际和生产动态,为蜀南地区茅口组有水气藏二次开发、落实动态储量基础提供了参考。此次裂缝系统动态储量计算新方法的探索,对准确评估此类复杂储集体动态储量具有重要的现实意义。

The Lower Permian gas reservoirs in Maokou Group, Shunan Block, Sichuan Basin, are featured by high heterogeneity, well developed fracture-cavity systems, active formation water, complex dynamic production characteristics, etc. In actual produc- tion, a part of the fracture system exhibits abnormal upward or downward sloping of falloff curves, which indicates the presence of complex reservoirs, abnormal energy replenishment, and reservoir space changes. However, conventional dynamic methods are mostly limited to dynamic reserves calculation for constant volume reservoirs. For fracture systems subject to reservoir space changes and formation water invasion, dynamic reserves calculations have great disparity and poor applicability. Therefore, in the case study of the Well $47 fracture system, we, according to the yield instability analysis, took into aeeount many factors such as reservoir geo- logic features, gas/water distribution models, dynamic performance, etc. and employed numerical value solution and the method of geological model detailing with the Topaze software. As a result, the dynamic reserves of local reservoirs at different development stages were thus worked out for this well. The calculations reflect the practical situation and dynamic characteristics and provide a reference for the secondary gas recovery from water-invaded reservoirs in this study area. This new method is of great practical sig nificance to the dynamic reserves assessment for similar complex reservoirs.